/*
 * Copyright (C) 2011 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the
 * License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
 * express or implied. See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtCompatible;

import java.util.Comparator;
import java.util.SortedSet;

import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Utilities for dealing with sorted collections of all types.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
final class SortedIterables
{
    private SortedIterables()
    {
    }

    /**
     * Returns {@code true} if {@code elements} is a sorted collection using an ordering equivalent to
     * {@code comparator}.
     */
    public static boolean hasSameComparator(Comparator<?> comparator, Iterable<?> elements)
    {
        checkNotNull(comparator);
        checkNotNull(elements);
        Comparator<?> comparator2;
        if (elements instanceof SortedSet)
        {
            comparator2 = comparator((SortedSet<?>) elements);
        }
        else if (elements instanceof SortedIterable)
        {
            comparator2 = ((SortedIterable<?>) elements).comparator();
        }
        else
        {
            return false;
        }
        return comparator.equals(comparator2);
    }

    @SuppressWarnings("unchecked")
    // if sortedSet.comparator() is null, the set must be naturally ordered
    public static <E extends @Nullable Object> Comparator<? super E> comparator(
            SortedSet<E> sortedSet)
    {
        Comparator<? super E> result = sortedSet.comparator();
        if (result == null)
        {
            result = (Comparator<? super E>) Ordering.natural();
        }
        return result;
    }
}
